Final Evaporation Control in reservoirs
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ASSESSMENT OF EVAPORATION LOSSES IN INDIA As per available records, assessment of evaporation losses in the country was first made by L.A. Ramdas and presented in Symposium of Evaporation control in 1966. The assessment was based on the following assumptions: Area of arid, Semi arid and long dry spell regions of India 2,000,000 Sq.Km.. Estimated water area in this region(1%) 20,000 Sq.Km.. Estimated area where film application may be feasible 2,000 Sq.Km.. The evaporation loss from the above area 6,000 MCM The National Commission on Agriculture (1976) had estimated that the annual evaporation losses from reservoir surfaces will be of the order of 50,000 MCM. Central Water Commission in their publication “Status Report on Evaporation Control in Reservoirs, 1988” had indicated that on an average there is a loss of about 450 MCM of water every month from an area of 2,000 Sq.Km.. which amounts to an annual loss of 5,400 MCM. The Water Management Forum (WMF), a national body of the Institution of Engineers (India), in their publication “Water Conservation by Evaporation Control, 1988” had indicated that on the Indian sub-continent the estimate total loss of water from large, medium and small storages will be to the tune of 60,000 MCM, which according to WMF would be adequate to meet the entire municipal and rural water needs of India by 2000 AD. The assessment of evaporation losses had been reviewed by CWC in 1990. Average annual evaporation from reservoirs/water bodies in India varies from 150 cm to 300 cm. The total surface area of existing large and medium storages, tanks and lakes in the country is of the order of 12,000 Sq.Km.. This is likely to increase to about 25,000 Sq.Km. at the ultimate stage of development. Assuming annual evaporation loss rate of 225 cm, the evaporation loss from existing water bodies works out to 27,000 MCM. In the ultimate stage, the evaporation losses may be of the order of 56,000 MCM. Thus, likely evaporation losses appear to be high, considering capital costs involved in creation of storages. It may not, however, be possible to take remedial measures of evapo-retardation on all storages/water bodies. Assuming even 20% of the above area falls in scarcity and drought areas, it may be necessary to tackle around 2,400 Sq.Km. of surface area in the present stage and about 5,000 Sq.Km.. at the ultimate stage. It is further seen that about 30% of evaporation retardation may be achieved by known evapo-retardation methods. Thus it may perhaps be possible to effect a saving to the extent of 1,620 MCM at present and 3,375 MCM at the ultimate stage. Further reduction in evaporation losses may be possible with development of cost effective and economic methods of evapo-retardation. |
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